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Studies dedicated to the homogenization approach of microcracked media are largely focused on the determination of effective elastic properties. Some works investigate other properties, but most of them consider only open cracks. This paper intends to provide effective thermal properties related to the conduction problem taking into account the unilateral effect (opening/closure of cracks). Such analysis considers steady-state heat transfer within an initially isotropic media weakened by randomly oriented cracks. According to the boundary conditions, estimates and bounds based on Eshelby-like formalism are developed to derive closed-form expressions for effective thermal conductivity and resistivity in a fixed microcracking state. [ABSTRACT FROM AUTHOR]

The survival probability of a tree exposed to surface fire varies widely depending on its bark. To advance the understanding of insulation properties of bark, mean thickness (BT), moisture content (MCb), surface structure (BS) and density (ρb) of bark samples of Mongolian oak (Quercus mongolica) (n = 395) for four diameter classes were investigated. In addition, data from 158 heating experiments simulating low-intensity surface fires in the laboratory were used to assess the relative importance of these properties affecting thermal insulation and evaluate the applicability of two stem heating models, an analytical, one-dimensional model and the FireStem2D model. Overall, BT is the best predictor of bark insulation capacity and MCb only contributes significantly to explain the residence time of cambial temperature >60°C (τ >60), whereas ρb and BS have minor effects. Although the two stem heating models overestimate the time required for cambium temperatures to reach 60°C (τ 60), FireStem2D performed better than analytical model. Furthermore, FireStem2D provides good predictions of τ >60 and maximal cambial temperature (T max). In addition, errors in FireStem2D may be driven mainly by the errors in temperature measurement and the limitation of a two-dimensional model. The study provides a better knowledge of interactions between bark properties and heat transfer, which may improve the predictability of fire-caused stem injury for Mongolian oak and other species with similar bark properties. Bark thickness is a better predictor of bark resistance to heating than bark moisture, surface structure and density. FireStem2D, a numerical model incorporating bark thermal properties and heat transfer mechanisms, performs better than traditional analytical model in prediction of cambial injury. [ABSTRACT FROM AUTHOR]

The evaluation of thermal-wet properties contributes to the research and development of fabrics, but there is no effective method to address and achieve evaluation of the hygroscopic and cooling properties of knitted fabrics to date. Therefore, an evaluation method aiming at this issue was proposed, and based on experimental investigation the hygroscopic and cooling property of fabrics was estimated by the combined evaluation of moisture management and the thermal property in a dynamic state. The moisture management property shows the liquid water absorption and diffusion performance of fabrics. Beside this, the thermal properties of fabrics were tested respectively in the dry and wet states. The thermal property of dry fabric showed the heat transfer and radiation of fabric itself, whereas the thermal property of wet fabric demonstrated the combined effect of the coupled heat–moisture property of wet fabric and the cooling function of moisture evaporation and diffusion. Furthermore, the thermal properties of fabrics were tested using a YG606 II thermal resistance tester, which was refitted by a program to control heating power. Eight knitted fabric samples having different cooling comfortability rates or values were selected to verify the feasibility and effectivity of this method. The consistency of this method was also verified by the obtained experimental results. Based on the obtained results, it can be observed that this method was well consistent with verified experimental results. Therefore, an effective method for the evaluation of hygroscopic and cooling knitted fabrics was obtained that satisfies the measurement of performance, and desirable fabric properties can be achieved for various applications. [ABSTRACT FROM AUTHOR]

In this article, thermal analysis of radial moving fins of hyperbolic and rectangular profiles is performed. A time-dependent nonlinear differential equation modeling heat transfer in a radial moving fin is considered. The thermal conductivity and heat transfer coefficient are modeled as linear and power-law functions of temperature, respectively. The analytical solutions are generated using the differential transform method which is an analytical solution technique that can be applied to various types of differential equations. The accuracy of the analytical solutions is validated by benchmarking against the numerical solutions obtained by applying the inbuilt numerical solver in Maple (pdsolve). A good agreement is observed between the analytical and numerical solutions. The effects of embedding parameters on the dimensionless temperature and heat transfer rate are analyzed. The results show that the fin rapidly dissipates heat to the surrounding fluid with an increase in the speed of the moving fin, that is, an increase in the values of the Peclet number. The results also show that the heat transfer through a rectangular fin is more efficient when compared to a fin of hyperbolic profile. [ABSTRACT FROM AUTHOR]

The bio-based materials have experienced in recent years a relevant evolution in construction and for many building applications. Despite the efforts to develop new solutions to achieve the objectives of numerical characterizations, a few researches in this area have been carried out using a heterogeneous wood-cement composite. This study is based on a constructive approach using the finite volume method in order to generate a numerical model capable of reproducing the equivalent transfer properties of a wood-cement composite. The challenge is to understand, design, and control this multiphase inhomogeneous structure and predict transfers and flows within the community in order to achieve an optimal functionality. Experimental measurements and microscopic characterization using X-ray microtomography were performed to compare and demonstrate the method validation. The comparative results demonstrate a less than 10% deviation between the measurements and the simulations of the equivalent thermal properties. Thus, thermal conductivity and permeability, under different medium configurations, were characterized. Therefore, it was observed that these properties depend strongly on the porosity and the pore distribution in the continuous phase. Moreover, these two parameters are highly dependent on cement percentages in the structure. [ABSTRACT FROM AUTHOR]

This paper studies the heat-shielding performance of a beetle forewing to explore how it has excellent thermal protective properties. With an experimental setup of a self-developed heating environment, the heat transfer characteristics of the beetle forewing were tested at 50°C under steady state conditions. Two types of the forewings are considered: cut wing and live wing. The heat transfer results show that the live forewing provides a good heat-shielding performance with the heat-shielding index stabilizing at around 22.1%, which is 60% higher than that of the cut wing. Based on scanning electron microscope images of the microstructure of the cross section of the beetle forewing, a simplified finite element analysis is performed to numerically calculate the heat transfer properties of the forewing. The numerical simulations reveal that the proposed structure of the forewing is good for the design of an effective thermal protection system. In addition, the uncertainty analysis is performed to evaluate the quality of experimental data. These results provide a foundational understanding of the heat transfer characteristics of beetle forewing, which will inspire a promising candidate for an actively cooled thermal protection systems. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this paper is to investigate the thermal transfer properties of electric heating fabric system which contains heating units or conductive yarns by numerical simulation, in order to optimize and evaluate the thermal performance of heating clothing. Design/methodology/approach: Two kinds of FEM models are created by ANSYS system: macro-scale models of the fabrics system with heating units and air layer; and meso-scale models of the plain-woven fabrics were established embedded with the stainless yarns. In the macro-scale model, the interior and surface temperature field distribution were simulated and analyzed based on different heating unit size, heating power, heating region, air layer thickness and ambient temperature. For meso-scale models, the effects of the conductive yarns temperature, covering fabrics and pore-filling material on the temperature field distribution were simulated and analyzed. Findings: With the increasing of the air layer thickness or the effective conductivity, the heat transfer along the direction of fabric thickness decreases gradually. The heat transfer along the fabric plane can be increased by dispersing the heating region. With the increasing of the conductive yarns' temperature or the covering fabrics' conductivity, the heat transfer distance along the fabric warp direction can be increased. Filling the internal pores of the fabric with 10 wt% SiC/TPU hybrid materials can effectively increase the in-plane heat transfer and improve the temperature uniformity on the surface of heated fabrics. Originality/value: The finite element method was used to establish the simulation models of the heating fabric systems. The influence of several parameters on the thermal performance was analyzed and discussed, as well as the internal and external temperature distribution in the macro and micro scales models. [ABSTRACT FROM AUTHOR]

The heat transmission through a fabric during the measurement of thermal resistance was simulated by a novel heterogeneous model that was constructed according to the structure of ThermolabII Tester KES-F7. In this model, the heat transmissions along the longitudinal and transverse directions of yarn were treated independently. The material constants of fabrics, such as mass density, specific heat, thermal conductivity and thickness, were used as parameters for simulation in this fabric model. The validity of this model was then confirmed by the high consistency between the heat flux obtained from experiment and simulation, with the average difference ratio lower than 5%. The simulation results suggested that the guard area could effectively reduce the horizontal heat leakage from the test plate when the experimental fabric was thin. Only less than 8% of heat leaked in the one-layer case, while the leakage was significantly aggravated when more layers of fabric were stacked, resulting in the considerably lower thermal insulation achieved in both experiment and simulation compared with that in real fabrics. The temperature distribution in the model also implied that the longitudinal and transverse thermal conductivity of yarn exerted great effect on the heat leakage during the measurement. Moreover, for multilayers consisting of different fabrics, the laying sequence could obviously influence the heat leakage and, consequently, change the obtained thermal resistance. [ABSTRACT FROM AUTHOR]

• Lightweight, thermostable and strong SiC aerogels are fabricated from biomass. • The SiC aerogels have highly interconnected porous structure decorated with in situ grown SiC nanowires. • The SiC aerogels exhibit superior EM wave absorption, thermal insulation properties and mechanical stability. • The effects of structure on the enhanced performance are thoroughly revealed. Lightweight and strong silicon carbide (SiC) aerogels with a three-dimensional architecture and in situ grown SiC nanowires are obtained from natural eggplants by direct graphitization and subsequent carbothermal reduction. Effective synergism is achieved by decorating the SiC frameworks with one-dimensional SiC nanowires, which impart the aerogels with excellent electromagnetic (EM) wave absorption, thermal insulation, and mechanical properties. Highly porous, interconnected SiC networks facilitate the multiple reflection–absorption effects of infiltrated EM waves and extend the routes of heat transmission in the samples. SiC nanowires, which consist of numerous stacking faults and heterojunctions, play key roles in dissipating EM energy, obstructing heat transfer, and reinforcing the SiC skeleton. Given their 97.6% porosity, the SiC aerogels show a minimum reflection of −43 dB and effective bandwidth of 4 GHz at 2 mm thickness. The in situ grown SiC nanowires substantially increase the compressive stress of the SiC aerogels to 2.12 MPa, which is nearly 50-fold than that of carbon aerogels derived from eggplants. Moreover, the SiC aerogels show a very low thermal conductivity of 0.035 W/m·K. These results indicate that the developed SiC aerogels are outstanding materials with potential applications in high-performance EM absorption and thermal insulation in the aviation and aerospace fields. [ABSTRACT FROM AUTHOR]

Series of NaBa 0.97 Ce 0.03 B 9 O 15 : x Tb3+, y Sm3+, z Dy3+ are synthesized by the traditional high temperature solid-state method. Ce3+ is used as a sensitizer to improve the spectral properties of Tb3+, Sm3+ and Dy3+ by the way of energy transfer which is proved by the fluorescence decay curves. And the mechanisms of energy transfer from Ce3+ to Tb3+, Sm3+ and Dy3+ are all determined as dipole-dipole interaction. The color of NBB:3%Ce3+, x Tb3+, 0.5%Sm3+ can shift from light violet thought white to yellow. And NBB:3%Ce3+, z Dy3+ can give out white light and move to green field. Moreover, the thermal stability makes NBB:3%Ce3+, 0.2%Dy3+ be a potential candidate for the self-referencing luminescent thermometry. Image 1 [ABSTRACT FROM AUTHOR]

To improve the performance and increase the lifetime of oil‐filled transformers, the thermal and dielectric properties of the transformer oil should be enhanced. Recently, nanotechnology was used as an effective science in the field of transformer oil development. In this study, barium titanate (BT) nanoparticles were inserted into the base transformer oil by a concentration of 0.005 g/L as an individual nanofluid sample (INFS). This insertion enhances the heat transfer coefficient by 33% but the breakdown voltage (BDV) was decreased by >10%. To overcome this problem of dielectric properties degradation, other three hybrid nanofluid samples (HNFS) were prepared using three different types of metal oxide (MO) nanoparticles; titania, alumina, and silica. These samples were prepared by adding a concentration 0.01 g/L of MO nanoparticles together with 0.005 g/L of BT nanoparticles into the oil. The thermal and dielectric properties of HNFS were measured to study the behaviour of nanoparticles hybridisation on transformer oil properties. HNFS using titania nanoparticles provided the best composition regarding either BDV or heat transfer coefficient. Dynamic light scattering (DLS) technique was used to evaluate the particle size distribution of hybrid nanoparticles and to clarify the corresponding physical mechanisms behind the obtained enhancement. [ABSTRACT FROM AUTHOR]

Mass diffusion of rhodamine 6G (R6G) in water-based alumina nanofluids is studied by means of total internal reflection fluorescence (TIRF) microscopy. We report a mass diffusivity enhancement that reaches an order of magnitude in a 2 vol % nanofluid when compared to the value in deionized water. Since experiments were performed with positively charged R6G, interfacial complexation between the dye and the nanoparticles was not observed. The effect of local density variations on mass diffusivity measurements is also addressed. An explanation for the enhancement of mass diffusion is presented using arguments based on dispersion, and it is shown that it correctly describes the order of magnitude differences between the thermal conductivity and mass diffusivity enhancements reported in the literature. [ABSTRACT FROM AUTHOR]

We investigated the effect of Bi doping on magnetic and magnetocaloric properties of La0.7-xBixSr0.3MnO3 (x=0.0-0.4). It is shown that the low temperature ground state changes from a ferromagnet (x=0) to a charge-ordered antiferromagnet for x=0.4. While the paramagnetic-ferromagnetic (PM-FM) transition is second-order in x⩽0.25, it changes into first-order for x=0.3 which is at the magnetic phase boundary. The changes in the magnetic ground state affect magnetic entropy. The magnitude of the isothermal magnetic entropy (/ΔSM/) at the FM Curie temperature increases from 4.56 J/kg K for x=0 to a maximum value of 5.02 J/kg K for x=0.05 and then decreases to nearly zero for x=0.4 at the charge order transition. In contrast to x⩽0.25, the ΔSM of x=0.3 is magnetic history dependent and its temperature dependence exhibits a clear step at TCO=260 K followed by a plateau between 240 and 185 K. Although (/ΔSM/) =3.1 J /kg K of x=0.3 is small compared to other compositions, it has a high relative cooling power (325 J/kg) which is desirable for magnetic refrigeration over a wide temperature. The unusual magnetic and magnetocaloric properties of x=0.3 are attributed to the existence of short-range charge-orbital (CO) correlations in the PM state. It is suggested that harnessing competition between FM spin ordering and CO correlations may provide a strategy to enhance magnetic refrigeration capacity over a wide temperature range. [ABSTRACT FROM AUTHOR]

Nanofluids have shown remarkable attraction in heat transfer community due to its reported enhanced thermal properties. One factor which can restrict nanofluids in heat transfer application is the increased viscosity value (compared to classical predictions). Particle aggregation occurring was the major reason for this observation. Even though majority of the aqueous nanofluids prepared in literature were stabilized electrostatically by adjusting the pH, studies on the effect of the electrical double layer thus created and its influence on viscosity increase has not been investigated for these nanofluids so far. Thus, in the present paper, rheological properties of alumina-water nanofluids, which are electrostatically stabilized, are measured and the increase in suspension viscosity due to presence of this electrical double layer causing additional electroviscous effects is brought out. Based on dynamic light scattering studies, particle agglomeration and its subsequent effect in increasing the viscosity of alumina-ethylene glycol nanofluid, where electroviscous effects are absent, are also considered. It is noted that the understanding of electroviscous effect is equally important as understanding the particle agglomeration effect and understanding both the effects is central to revealing the physics of nanofluid rheology. Further, hydrodynamic experiments are made, which show that nanofluids behaves almost like a homogeneous fluids under flow conditions, and by knowing their properties, such as viscosity and density, pressure drop can be predicted. [ABSTRACT FROM AUTHOR]

A front-surface measurement for determining the thermal properties of thermal barrier coatings has been applied to air plasma spray coatings. The measurement is used to determine all independent thermal properties of the coating simultaneously. Furthermore, with minimal requirements placed on the sample and zero sample preparation, measurements can be made under previously impossible conditions, such as on serviceable engine parts. Previous application of this technique was limited to relatively thin coatings, where a one-dimensional heat transfer model is applied. In this paper, the influence of heat spreading on the measurement of thicker coatings is investigated with the development of a two-dimensional heat transfer model. [ABSTRACT FROM AUTHOR]

A midinfrared quantum cascade laser with Mach–Zehnder cavity and split contacts is investigated with respect to interference effects. By increasing the temperature in one of the two coupled active waveguides, the value of the effective refractive index is varied and the modal phase is shifted. As a result, destructive interference is observed within the resonator, which manifests itself in a minimum of the modulated output power. The dissipated heat is controlled by locally adding a continuous current to the drive current pulses. In the first step, thermal properties, threshold values, and far fields are analyzed and compared to a Fabry–Pérot resonator to gain insight into the physical principles of the monolithic interferometer. Based on these findings, the temperature distribution is calculated in a two-dimensional heat transfer simulation, which leads to a match between the thermal change of the effective refractive index and the condition for destructive interference; a phase shift of π between the two interfering beams is confirmed. By modulating the effective refractive index using evanescent fields instead of temperature variations, a monolithic midinfrared interferometric sensing device becomes feasible. [ABSTRACT FROM AUTHOR]

Computationally efficient heat transfer models of keyhole mode laser welding ignore fluid flow in the gas, liquid, and the two phase solid-liquid regions. These models cannot be applied to high Peclet number systems where convective heat transfer affects weld pool geometry, cooling rate, and other weld attributes. Here we show that by synthesizing features of an existing model to determine keyhole shape and size with rigorous fluid flow and heat transfer calculations in the liquid and the two phase solid-liquid regions, important features of both high and low Peclet number systems can be satisfactorily simulated. The geometry of the keyhole is calculated by assuming thermal equilibrium at the gas/liquid interface and point by point heat balance at the keyhole wall. The heat transfer outside the vapor cavity is calculated by numerically solving the equations of conservation of mass, momentum, and energy. A vorticity based turbulence model is used to estimate the values of effective viscosity and effective thermal conductivity of the liquid metal in the weld pool. It is shown that the temperature profile and the weld pool shape and size depend strongly on the convective heat transfer for low thermal conductivity alloys like stainless steel. For high thermal conductivity aluminum alloys, on the other hand, convection does not play a significant role in determining the shape and size of the weld pool. The computed solidification parameters indicated that the solidification structure becomes less dendritic and coarser with the decrease in welding velocity. The results demonstrate that a numerically efficient convective heat transfer model of keyhole mode laser welding can significantly improve the current understanding of weld attributes for different materials with widely different thermal properties. [ABSTRACT FROM AUTHOR]

By taking into account the interfacial thermal resistance across the solid particles and the host liquids, we present differential effective medium theory to estimate the effective thermal conductivity in nanofluids of nonspherical solid particles. It is found that high enhancement of effective thermal conductivity can be achieved when the nanoparticles’ shape is deviated much from the spherical one. On the other hand, increasing the interfacial thermal resistance results in an appreciable degradation in the thermal conductivity enhancement. To one’s interest, our theoretical results are in good agreement with recent experimental data on nanofluids. In particular, our theoretical predictions successfully show the nonlinear dependence of effective thermal conductivity on the volume fractions of nanotubes. [ABSTRACT FROM AUTHOR]

The traditional bottom liquid-cooling thermal management system (TMS) has poor cooling performance and is prone to causing significant temperature difference in the lithium-ion battery (LIB) module. In order to solve the above problems, this study takes the Z-shaped micro heat pipe array (MHPA) as the core heat transfer element and establishes a top liquid-cooling (TLC) TMS based on Z-shaped MHPA. The thermal management performance of the TLC TMS based on Z-shaped MHPA is analyzed by comparing it with the traditional bottom liquid-cooling TMS. Results show that under the conditions of 40 °C ambient temperature and 25 °C cold water inlet temperature, the bottom liquid-cooling TMS can no longer meet the thermal management requirements of the module at a 2C charge–discharge rate. In comparison, the TLC TMS based on Z-shaped MHPA can ensure the module's maximum temperature below 55 °C, and the battery and module level's temperature difference can be controlled below 4 °C under 3C charge–discharge rate. The TLC TMS based on Z-shaped MHPA can not only effectively delay the battery's temperature rise under high charge–discharge rate, but also significantly reduce the temperature difference; its thermal management performance is significantly better than the bottom liquid-cooling TMS. • A top liquid-cooling TMS based on Z-shaped MHPA is presented. • This design provides excellent thermal management performance. • This design is safety and easy to combine with the battery swap mode. [ABSTRACT FROM AUTHOR]

An inverse heat transfer approach for predicting the moving freezing front and the temperature distribution inside tumors during cryosurgery is presented. By recording the time-varying temperature at the surface of the diseased tissues, the inverse method is able to estimate simultaneously the blood perfusion rate and the metabolic heat generation of the tumor. Once these thermal properties are determined, the temperature field and the moving freezing front are predicted with a direct method. The direct problem is solved with the one-dimension Pennes bioheat equation and the enthalpy method. The inverse model rests on the Levenberg-Marquardt Method (LMM) combined to the Broyden Method (BM). The following effects on the predictions of the inverse method are investigated: (i) the initialization of the unknown thermal properties; (ii) the thermal properties of the diseased tissues; (iii) the duration of cryosurgery; (iv) the temperature of the cryoprobe; (v) the noise level on the recorded temperatures; and (vi) the total number of recorded data. It is shown that the proposed inverse method remains accurate and stable for all cases investigated. Recommendations are made for the initialization of the parameters of the inverse method and for the total number of measurements. [Display omitted] • A promising alternative to MRI and ultrasound for controlling the motion of the freezing front during cryosurgery is proposed. • A non-isothermal phase change process of freezing tissues is developed. • The inverse approach is able to predict the blood perfusion rate and the metabolic heat generation during cryosurgery. • The effect of the most influential parameters on the inverse predictions is examined. [ABSTRACT FROM AUTHOR]

[Display omitted] • The thermally conductive HDPE/BN/CNT composite was fabricated by an in-house Rotational Shear System. • The interlocking crystal structure improves thermomechanical properties. • Constructing the ternary synergistic network of aligned BN, shish-kebab and elongated CNT. • The thermal conductivity of RB20C5 reach as 2.37 W/mK with higher Heat transfer efficiency in hoop direction. Fabricating polymer composites with excellent thermomechanical properties remains a challenge due to the tradeoff between high filler loading and loss of strength. Conventional composites made of randomly oriented lamellae and aggregated fillers fail to construct thermally conductive pathways for filler-filler or filler-crystal contacts. To address this issue, a synergistically ternary network composed of aligned BN and elongated CNT in a shish-kebab structure has been prepared by an in-house Rotation Shear System (RSS). The composite with 20 wt% BN and 5 wt% CNT achieved a high thermal conductivity of 2.37 W/(mK) under shear modification. The tensile strength and Vicat softening temperature of the composite are 2.29 times higher and 21.9 °C greater than those of unsheared samples. Such superior thermal and mechanical properties are mainly attributed to the interlocking shish-kebab structure, which serves as a support skeleton in composites, where aligned BN and CNT construct a heat-resistant barrier. This work provides an effective strategy to fabricate high thermally conductive composites with excellent mechanical properties, providing new insights into reducing material replacement frequency under extreme operating conditions. [ABSTRACT FROM AUTHOR]

• The sensitivity of thermal response tests using resistively heated methods under various setups is demonstrated. • The effect of test setups on estimation results is examined using numerically generated data. • A distance-based generalized sensitivity analysis method is employed. • The in-situ design strategy of the novel tests is illustrated combining sensitivity analysis and field tests. Thermal response tests employing resistively heated methods (TRT-RH) have shown advanced performance in evaluating ground properties, while the effect of various TRT-RH setups is still vague in practice. This study examines the effect of different TRT-RH setups based on numerically generated data and field data. As a result, the various setups alter the heat transfer and change the test time required to meet the ideal linear heat source (ILHS) assumption. Time thresholds that indicate TRT-RH are positively related to eccentric distance, negatively related to borehole radius, and positively related to grout thermal conductivity difference. The distance-based general sensitivity analysis result shows that the radius of the borehole or trench, which separates the heat source and the ground, has intensive sensitivity to the test effectivity. This study presents the standard setup strategy for TRT-RH to measure the thermal and hydraulic properties based on the ILHS assumption. [ABSTRACT FROM AUTHOR]

Silver (Ag) paste sintering is used as a die-bonding technology for the next generation of power electronic modules as Ag offers a high melting temperature as well as excellent thermal and electrical conductivities. Ag paste sintering is performed using specific conditions depending on the type of paste and the users' specifications (temperature, time, pressure), ending up in a porous joint. As a result, the properties of those joints are heavily influenced by their densities (i.e. porosity). Despite the numerous studies reported in the literature, the relationship between the density of the joint and its thermal conductivity remains an issue since access to the density of an embedded thin joint is very challenging. Furthermore, little is known on the evolution of the thermal conductivity in operating conditions. In this study, these issues were investigated by developing self-standing specimens with microstructures representative of those of real joints. In order to study a wide range of porosity, sintering was performed using a single time/temperature under various pressures. The thermal conductivity was measured using 3D flash method, consisting in applying a short non-uniform laser excitation on the surface of the sample, leading to three-dimensional heat transfer. The relationship between porosity and thermal conductivity is established for the as-sintered state and after aging up to 500 h at temperatures ranging from 150 °C to 350 °C and is compared to existing models. The evolution of the thermal properties during thermal aging is discussed considering both the elaboration conditions and the microstructure evolution. [Display omitted] [ABSTRACT FROM AUTHOR]

We discuss the ablation of aluminum plasma using picosecond pulsed laser in vacuum and in ambient atmosphere of nitrogen. The plume dynamics of picosecond and nanosecond laser-ablated plumes in ambient atmosphere is discussed. The degree of polarization is measured using optical emission spectroscopy for the Al III transition 4s 2S1/2-4p 2P3/2o at 569.6 nm. Strong anisotropy is observed using picosecond laser pulse as compared to nanosecond laser pulse. [ABSTRACT FROM AUTHOR]

The adobe is a widely used traditional material in popular constructions in rural areas of Peru and more generally in Andean countries. In order to increase comfort and energy efficiency of constructions, it is necessary to better know the thermal characteristics of the adobe, seen as a bio-composite material. Different adobes have been studied. Effective thermal conductivity and heat capacity were measured by means of a hot parallel-plate method. Density was estimated using a pycnometer and measuring physical dimensions and mass of each sample, which allowed the calculation of thermal effusivity and diffusivity. Some numerical simulation results displayed good agreement with experimental outcomes. The work presented here has implications for future studies of this traditional building material and might potentially help solving the problem of sustainable housing.

Presents information on a study which reported a theoretical model describing specific mechanisms of heat transport in as-prepared and oxidized meso-porous silicon layers. Thermal conductivity of silicon layers; Details of the micro-Raman scattering applied in the study; Features of the theoretical model; Conclusions.

The theoretical analysis of different concentrating photovoltaic and thermal systems (CPV/T) is presented in this paper; it allows to evaluate the cooling fluid temperature in different working conditions. In particular, two CPV/T systems with different optics, line-focus and point-focus, are studied and compared theoretically by means of a model developed in ANSYS-CFX able to evaluate the theoretical temperature values of the fluid that flows in the cooling circuit, designed with the Solidworks software. The comparison in terms of the thermal performances between the point-focus and line-focus configurations of a CPV/T system has been realized considering different working conditions. As model input the uniform cell temperature has been set to different values, included between 323 K and 363 K, or determined experimentally referring to the point-focus configuration. In particular, the outlet temperatures of the cooling fluid, the fluid and cells temperatures difference at the outlet section, the time necessary to reach a steady-state condition, the fluid temperature trend in different parts of the tube and along the circuit, have been evaluated. Moreover, the fluid temperature trend has been studied varying the fluid velocity, its mass flow rate, and the insulation thickness. Finally, the point-focus CPV/T system thermal performances have been also evaluated adopting some experimental measurements as input data; the fluid temperature trend has been tested under a variable cell temperature during different hours of a sunny and a cloudy day. [ABSTRACT FROM AUTHOR]

Summary: For electronic thermal management with hydrated salt phase change materials (PCM), supercooling and thermal stability usually inhibit its development. In view of this, novel of disodium hydrogen phosphate dodecahydrate (DSP)‐based composites PCM with miniaturized size is developed to solve these problems. Three kinds of carbon fillers employed as both nucleating agent and heat transfer promoter were added in DSP separately. The influences of carbon fillers' specific surface area, particle size, and adsorption mode on thermal properties of DSP‐based composites PCM were investigated experimentally. The thermal conductive chains of composites PCM were detected by energy dispersive spectroscopy. The supercooling degree was analyzed by melting‐freezing test. Temperature‐regulated property was captured by infrared imager. In the present work, the supercooling degree of GNS/DSP composites PCM is efficiently reduced to 97.24% compared with the pure DSP. Negligible change in phase change temperature of the CNTS/DSP composites PCM was confirmed after 200 times cycles. There was no obvious liquid leakage of DSP when 2 wt% of carbon fillers were added in composites PCM. The enhancement on thermal properties of DSP is a promising strategy for numerous thermal applications. [ABSTRACT FROM AUTHOR]

Highlights • Presents theoretical solution for a phase change heat transfer problem. • Utilizes perturbation method and an iterative approach. • Results may be helpful in analyzing phase change heat transfer in energy storage. • Results expand our theoretical understanding of phase change heat transfer. Abstract Heat transfer problems involving phase change occur in a wide variety of engineering applications. Except a few simple cases, most phase change problems do not have an exact solution, and a number of approximate analytical methods have been developed. This paper presents a theoretical solution for a one-dimensional phase change problem that includes a pre-melted or pre-solidified length between the region of interest and a time-dependent temperature boundary condition. Such a scenario can occur in multiple engineering applications when the heating or cooling process is intermittent in time. The theoretical approach involves iteratively solving the coupled problem involving thermal conduction and phase change, utilizing a perturbation-based method for the phase change problem with a time-dependent boundary condition. The resulting theoretical solution compares well with numerical simulations. Results are used for analyzing the effect of geometry, thermal properties and other parameters on the nature of heat transfer and phase change in this problem of much technological importance. These insights may be helpful in analyzing and optimizing heat transfer in several applications such as phase change based cooling of Li-ion cells during intermittent operation. [ABSTRACT FROM AUTHOR]

Abstract How to effectively enhance the flame retardancy of polyamide 46/polyphenylene oxide (PA46/PPO) alloy is one of the key issues needed to be addressed. In this work, organic-modified zirconium phosphate (OZrP) nanosheet was incorporated with PU-coated carbon fiber (CF) to flame-retard PA46/PPO alloy. The combination of OZrP and CF showed an outstanding combination effect in improving the flame retardancy and thermal stability of PA46/PPO. With the incorporation of 2 wt% OZrP and 20 wt% CF, the peak heat release rate and peak smoke production rate of PA46/PPO were reduced by 65.6% and 86.2%, respectively. Besides, the T i (temperature at 5% weight loss) and the residue of PA46/PPO/OZrP/CF were increased by 13.2 °C and 20.9 wt%, respectively, compared with PA46/PPO. The flame-retardant mechanism was further studied and revealed: when being burned, CF acted as the skeleton to improve the strength of char; simultaneously, OZrP catalyzed the carbonization of the polymer chains on the CF surface to form a strong and compact protective char layer, which blocked the transmission of heat and combustible gases, thus effectively improved the flame retardancy of the composite. Highlights • An efficient strategy simultaneously improving the flame retardancy and mechanical properties of PA46/PPO alloy was proposed. • The synergistic mechanism of OZrP nanosheet and PU-coated carbon fiber (CF) on the flame retardancy of PA46/PPO was revealed. • OZrP catalyzed the carbonization of the polymer chains on the CF surface to form a strong and compact protective char layer. [ABSTRACT FROM AUTHOR]

The aim of this study was to assess the variation of physiological responses and mortality of day-old chicks subjected to different thermal conditions and exposure times during simulated transport. For this purpose, day-old chicks (n = 900) were used and subjected to simulated conditions of transport in a climate chamber. The experimental design was a completely randomized block design, with the structure of the treatments in a 3 × 3 factorial scheme (thermal ranges and time intervals) and each level of containers considered a block. The physiological variables used in this trial were body weight, respiratory rate, cloacal temperature, average surface temperature, and gene expression of heat shock protein (HSP70). Regarding body weight, a small variation was observed between treatments (P > 0.05). The animals subjected to the heat treatment exhibited respiratory rates above 100 movements per minute (P < 0.05), average cloacal temperatures above 44.7 °C, surface temperatures above the comfort zone (greater than 39.6 °C; P < 0.05), and increased gene expression of HSP70 (P < 0.001), especially after 3 initial hours of exposure. In addition, the heat treatment lead to increased mortality of the animals (over 6%). Also in the cold treatment, despite the absence of mortality, the animals showed hypothermia from 3 h of exposure, based on the results of the average surface (28 °C) and cloacal temperatures (39.6 °C; P < 0.05). In this way, the results imply that the effects of thermal stress caused by heat as well as by cold in a simulated transport condition are increased when traveling for more than 3 h, indicating a trend of rising mortality after long-term transportation of day-old chickens. [ABSTRACT FROM AUTHOR]

Abstract In the present work, an experimental investigation was conducted to quantify the heat transfer coefficient, thermal resistance and the thermal performance of a thermosyphon heat pipe charged with zirconia-acetone nanofluid. The thermosyphon was designed to operate at high heat fluxes such as 200 kW/m2 (∼200 sun) similar or larger than the evacuated solar tube heat pipes. The zirconia-acetone nanofluid was prepared and stabilized by adding a surfactant, homogenizing with sonication and setting the pH of the nanofluid with a buffer solution. The thermosyphon was fabricated with an oxygen-free copper with the internal and outer diameters of 10.7 mm and 12 mm, respectively and the axial length of 280 mm. The thermal performance of the heat pipe was assessed for various heat fluxes (1 kW/m2-200 kW/m2), filling ratio (20%–75%), tilt angle (5°–70°) and the mass fraction of the nanofluid (0.025%–0.1%). Results showed that the presence of the nanofluid decreases the total thermal resistance of the heat pipe reaching the minimum value at the largest heat flux applied to the evaporator. Also, the heat transfer coefficient of the evaporator was increased. Likewise, the zirconia-acetone nanofluid enhanced the boiling heat transfer mechanism and the geyser boiling, which resulted in the enhancement in the thermal performance of the heat pipe due to the increase in the heat transfer coefficient of the heat pipe by 36.3% at wt. % = 0.1 in comparison with the pure acetone. The optimum tilt angle and filling ratio values were 65° and 60%, respectively, in which the highest heat transfer coefficient was achieved. A correlation was also developed using a dimensionless analysis to predict the Kutateladze number as an index for the thermal performance of the heat pipe. Highlights • Zirconia-acetone nanofluid was assessed in a thermosyphon. • Nucleate boiling and geyser boiling were the dominant heat transfer mechanisms. • A tradeoff between filling ratio, tilt angle and performance was identified. • A new correlation was developed for estimating Kutateladze number. • The boiling HTC was in a good agreement with Stephan-Abdelsalam equation. [ABSTRACT FROM AUTHOR]

The determination of local convective heat transfer coefficients in microfluidics is a very hard task. Due to the small dimensions of channels and walls, the use of conventional measurement techniques is only partially suitable in microfluidics. For this reason, a strong effort has been made during the last decades in order to propose innovative techniques which use internal (to microdevices) sensors of reduced dimensions and/or external conventional sensors. In this paper a review of the main experimental techniques proposed for the determination of the local near-wall fluid temperature, the local wall temperature, and the local fluid bulk temperature will be given by putting in evidence for each technique's positive and negative aspects as well as their actual limitations with the aim to stimulate and address the research on this topic in the near future. The problems and the limitations existing nowadays for the accurate measurements of the local thermal properties of a convective microflow demonstrate that for the analysis of microconvection experimental data have to be always integrated by a numerical modeling of the observed system. [ABSTRACT FROM AUTHOR]

Abstract This paper presents the quasi-stationary Wilson-Rosenthal solution for isothermal contours in a semi-infinite medium due to a moving heat source. There is a single dimensionless governing parameter which could correspond, for example, to a conduction-limited heat flow in a point-source driven, fusion process, such as that witnessed in modern metal additive processes. Variables involved in this heat transfer problem are the power and speed of the heat source as well as the thermal properties of the domain being heated. On one hand, the forwardmost location for a generic isothermal contour profile, for example the melting isotherm, is calculated by (i) a fixed-point numerical method, (ii) second-, third- and fourth-order Taylor series expansions, and (iii) a direct calculation of the location using the Laplace-Carson transform and an approximate anti-transform. On the other hand, the rearmost point of the isothermal contour is found to be invariant with the source speed parameter while the horizontal coordinate corresponding to the maximum depth of the contour is predicted by the semi-sum of the forwardmost and rearmost coordinates. Experimental results suggest that this analytical solution provides accurate physical understanding of the process, for example, when the melt pool contour geometry of a conduction-limited fusion process requires to be controlled during an specific heat driven process. In this latter situation, a single dimensionless governing parameter can be of benefit. [ABSTRACT FROM AUTHOR]

An experimental study is carried out in order to determine the thermal performances of a water-cooled heat pipe cooling system. An experiment rig is designed, fabricated and fully instrumented to test the cooling system prototype. The results show that the maximum heat transport capacity of the heat pipe increase with the water-cooling temperature; however, its overall thermal resistance decreases. Correlations for heat transfer in the evaporator and condenser sections are proposed. A model is also developed in order to determine the capillary limit as well as the heat transfer in the heat pipe. The model can predict the experimental results within -1.7 % and +7.9 % when estimating the capillary limit and underestimates the heat pipe overall thermal resistance within -17.8 % and -9.7 %; however, it overestimates the evaporator temperature within 4.4 % and 9.5 %. [ABSTRACT FROM AUTHOR]

The problem of conjugate natural convection flow in a layer of porous media confined by two vertical thermally-conductive thick surfaces is studied. The local thermal nonequilibrium approach is employed for modelling the porous layer allowing for a difference in temperature between the porous structure and the fluid inside it. The basic equations for this investigation are transformed into a set of dimensionless equations. Then, the resulting equations are solved numerically by employing the finite element method. The obtained results are compared with published results in the open literature and are found to be in good agreement. The effects of the wall thermal conductivity parameter, fluid and porous interfacial convective heat transfer parameter and the Rayleigh number on the thermal behavior of the cavity are studied and analysed. The results show that increasing all of the above mentioned parameters results in increasing the heat transfer in the cavity. [ABSTRACT FROM AUTHOR]

• A PVT collector with a roll-bond absorber is designed for rural home application. • Thermo-laminating is a novel and convenient method for PV-absorber connection. • The validated PVT model can simulate the roll-bond PVT performance accurately. • The model is available for predicting the dynamic performance of PVT systems. This paper mainly investigated the performance of a low-cost roll-bond water-type photovoltaic thermal (PVT) collector from both experimental and modelling approaches under the climatic conditions of Sichuan Basin of China. The design and manufacturing process of the PVT prototype adopted the available commercial PV panels for convenience and for reducing the manufacturing cost. The experiment measured all the main properties of the developed PVT module. The excellent heat transfer performance of its roll-bond absorber plate was also validated by outdoor steady-state tests. Then, the steady-state numerical models were used to simulate the performance of the PVT prototype in TRNSYS. By comparing the simulation and experimental results, two robust models were selected which have their own advantages in charactering the thermal and electrical properties of the PVT collector. Through validating the numerical models with experimental data, the deviation between the simulated and the measured values was further reduced. In addition, a complete photovoltaic thermal–domestic hot water (PVT-DHW) system with such PVT collectors was developed in TRNSYS, by which the annual system output and efficiency were predicted and analysed. [ABSTRACT FROM AUTHOR]

Abstract The aim of the current paper is modeling the thermal performance factor of water under influence of functionalized multi-walled carbon nanotubes. For this purpose, artificial neural networks (ANNs) have been employed. The thermal performance factor of the nanofluid is related to the drop in pressure and heat transfer. Therefore, usually the data associated with it does not follow a specific trend. In such cases, the neural network can be used well. Here, an optimal neural network was designed with 65 neurons, the inputs of which were Reynolds number and volume fractions. Moreover, 78 data were used for modeling, which included 62 data for training and 16 data for testing the model. With the aim of evaluation of the precision of the modeling by ANN, the experimental results were compared with neural network outputs in all cases. The results revealed that optimal ANN model has adequate accurateness to predict the complex trend of thermal performance factor. Highlights • Modeling thermal performance factor of water under influence of functionalized MWCNTs. • Data associated with thermal performance factor does not follow a specific trend. • The experimental results were compared with neural network outputs in all cases. • Optimal ANN has adequate accurateness to predict the trend of thermal performance factor. • The maximum margin of deviation is about 1.8%. [ABSTRACT FROM AUTHOR]

Molten-salt-based nanofluids and ionic-liquid-based nanofluids are developed for thermal storage and heat transfer at relatively high temperatures, in the past few years. Preparation and stabilization techniques are briefly introduced firstly, and then, thermal properties, e.g., specific heat, thermal conductivity and viscosity, are summarized and discussed in detail. The properties are not only affected by the characteristics of nanomaterials and base fluids, but also affected by the synthesis method, such as the sonication intensity and duration. Some of the thermophysical property data are still incomplete, especially the thermal conductivity of molten-salt-based nanofluids, and properties of ionic-liquid-based nanofluids at high temperatures. While several literature works show that the Krieger–Dougherty model can well predict the viscosity, no general models for thermal conductivity and specific heat have been developed yet for both types of nanofluids. [ABSTRACT FROM AUTHOR]

Abstract This study proposes a novel ultra-thin aluminum flat heat pipe with thickness of 1.5 mm for the first time in order to satisfy the ever increasing requirements for cost-effective, physically compact and highly efficient thermal management solutions. The extruded aluminum tube contains multiple separate micro cavities that work as independent micro heat pipes and a two-level compressing process is applied to flatten the tube to the ideal thickness. Sintered aluminum fibers and aluminum fiber meshes with surface treatment are inserted into each cavity of the ultra-thin heat pipe as the extra wicks for comparison. The thermal response characteristics of the fabricated aluminum heat pipes, including the temperature uniformity, thermal resistance, and effects of wick structure and inclination angles, are fully investigated. Under large inclination angle (90°), the smooth heat pipe without any extra wick performs lower temperature difference, lower thermal resistance, and higher heat transport capacity compared to that with aluminum fiber wick whereas the heat pipes with wicks present superiority under smaller inclination angles (60° and 30°) due to the liquid backflow enhancement. Besides, comparative study also shows that wick structure optimization holds the potential to improve the thermal performance of this ultra-thin two-phase device. Highlights • Ultra-thin aluminum heat pipe with only 1.5 mm thickness is developed. • It contains multiple separate micro cavities working as independent heat pipes. • The thermal response characteristics are fully investigated. • Wick structure optimization holds potential to improve the thermal performance. [ABSTRACT FROM AUTHOR]

In this research, an experimental evaluation is conducted on the hydrothermal behavior of water-based manganese ferrite nanofluid flowing in a metal foam tube. For this purpose, manganese ferrite nanoparticles are synthesized, and X-ray diffraction and scanning electron microscopy are implemented to specify the samples for determination of phase and size of nanoparticles. The effects of Reynolds number, Prandtl number, and presence of MnFe2O4 nanoparticles inside the water on the Nusselt number and friction factor have been studied. The experimental analysis shows that the increment of Reynolds number, Prandtl number, and nanoparticles concentration improve the heat transfer performance. The maximum of 19.1% and 10.5% increase in Nusselt number and friction factor have been achieved respectively by dispersion of 2 wt% manganese ferrite nanoparticles inside the deionized water at Reynolds number of 1,000. A hydrothermal index is proposed to consider the thermal and hydrodynamic characteristics of the nanofluid, and it is attained that the convection heat transfer improvement dominates the pressure drop in this work. According to the experimental results, the Nusselt number and friction factor of the nanofluid is modeled as a function of Reynolds number, Prandtl number, and nanoparticles concentration using artificial neural network with an acceptable precision. [ABSTRACT FROM AUTHOR]

The thermal diffusivity is the key parameter that controls near‐surface temperature where periodic temperature variation is progressively attenuated and delayed with depth. This article presents the results of apparent thermal diffusivity using temperatures recorded by a bedrock temperature measurement network in the fault zones of western Sichuan. High sensitivity temperature sensors (10−4 K) were installed at a maximum depth reaching 30 m. The apparent thermal diffusivities were deduced from both amplitude damping and phase shifting of annual temperature variations between two different depths. Under pure conduction, the thermal diffusivity determined through the phase method (αΦ) should be equivalent to that determined through the amplitude method (αA), whereas effects of the upward (downward) water flow are evidently reflected in the amplitude decay to make αΦ larger (lesser) than αA. The discrepancy between αΦ and αA can thus be a tracer of water movement or convective heat transfer. The calculated αΦ of the measurement stations varies from 1.22 × 10−6 to 3.00 × 10−6 m2/s, and the estimated αA ranges from 0.93 × 10−6 to 2.41 × 10−6 m2/s. Two regimes of heat transfer underground were suggested from the results. Conductive heat transport prevails over the nonconductive processes at five stations, which is characterized by αΦ coincident with αA for the same depth pair. On the contrary, the values of αΦ differ from αA at six stations in the intersection area of the Y‐shaped fault system, implying that convective heat transfer also plays a comparably important role. This finding is consistent with the hot springs distribution of the area. The results also indicate that water moves upward with an average Darcy velocity of approximately −1 × 10−7 m/s in this region. Our research provides new evidence for the hydrothermal activity in the fault zones at the eastern margin of the Tibetan Plateau. [ABSTRACT FROM AUTHOR]

The procedure of numerical identification of thermophysical properties of concrete during its hardening is presented. Heat of cement hydration, thermal conductivity and specific heat are determined for purpose of modelling temperature evolution in massive concrete elements. The developed method is based on point temperature measurements in a cylindrical mould and the numerical solution of the inverse heat transfer problem by means of direct search optimization algorithm. The determined thermal characteristics of concrete are not constant and depend on the maturity of concrete. The procedure was verified on set of concrete mixes designed with Portland cement CEM I 42.5R and Portland-slag cement CEM II/B-S 32.5 N. Calcareous fly ash was also used for partial replacement of cement in the mixtures. The obtained results have been compared with experimentally measured temperature in concrete and a fair agreement has been found. [ABSTRACT FROM AUTHOR]

In this study, the shapes and materials of thermal meta-structures, which can suppress as much heat propagation as possible in a structure, were investigated using a three-dimensional finite-difference time-domain technique. The heat flux vibrating in the traveling direction could be suppressed using multiple layers of thermal meta-materials. The heat flux transferred through the gap between thermal meta-structures could also be efficiently suppressed by placing even-numbered layers of thermal meta-structures in a zigzag arrangement in a structure. When the air-based thermal meta-structures were increased from one to four layers, the temperature inside the structure could be reduced from 38.9 °C to 25.5 °C. Moreover, when water-, paraffin-, aerogel-, and air-based thermal meta-structures having different thermal conductivities, densities, and specific heat characteristics were applied to the structure, a temperature of 50 °C to one side led to temperatures of 35.7, 33.4, 25.7, and 25.5 °C on the other. In other words, the temperature of the concrete block with air-based and aerogel thermal meta-structures was more than 13 °C lower than that of a conventional concrete block (38.9 °C), confirming that the insulation effect obtained by suppressing heat transfer was significant. [ABSTRACT FROM AUTHOR]